using System;

public class Program

{

    public static void Main()

    {

         int first = 100;

         int second = 200;

        Console.WriteLine("Before Swap: first: " + first + " second: " + second );      

        swap(ref first, ref second);

        Console.WriteLine("first: " + first + " second: " + second );

    }

    public static void swap(ref int first, ref int second)

    {

        first = first + second;

        second = first - second;

        first = first - second;

    }

}